Ferritic stainless steel



rename STAINLESS STEEL Freeman J. Phillips, Pittsburgh, Pa., assignor toUnited States Steel Corporation, a corporation of New Jersey No Drawing.Application December 4, 1953, Serial No. 396,338

4 Claims. (Cl. 75-124) This invention relates to 9 to 11% chromiumstainless steels and more particularly to stainless steels of this gradethat are ferritic at all temperatures below 1200 C. and have acoeflicient of expansion closely approximating the coefi'icient ofexpansion of glass whereby glass can be fused and sealed thereto.

In sealing glass to metal, the temperature of the glass is raised tofusion point of glass, i. e., about 1200 C. to effect the seal. If theseal is to remain intact without shattering or placing undue strain onthe glass, the coefiicients of expansion of the glass and the metal mustbe closely matched on cooling, particularly throughout the range oftemperature of 530 to 30 C. Moreover, for many purposes such as conesfor television tubes and the like, it is necessary to form the metalarticles in a spinning operation. Due to their ready formability,chromium stainless steels of the 28-30% straight chromium type andmodified 17% grades of such steel have heretofore been used for suchpurpose. While such steels are quite satisfactory, they are quiteexpensive and it is therefore desirable to use cheaper grades of steel.I have discovered that the 9 to 11% grade of chromium stainless can beused for such purpose if modified as hereinafter set forth.

It is accordingly an object of the present invention to provide chromiumstainless steels suitable for forming by spinning and for sealing toglass containing less chromium than steels heretofore usable.

It is a further object of the present invention to provide a stainlesssteel of the 9 to 11% chromium type suitable for sealing to glass.

The foregoing and further objects of this invention will be apparentfrom the following invention which is directed generally to chromiumstainless steels containing 9 to 11% chromium.

Steels of this type are readily formable by spinning and aresuificiently oxidation resistant to make them desirable for use inapplication requiring that glass be sealed thereto. Moreover, they areconsiderably cheaper than steels heretofore used. They, however, formaustenite upon heating to high temperatures which partially transformsto martensite upon cooling. The accompanying changes in volume, causingan unfavorable coefiicient of expansion render them unsuitable forsealing to glass. To be suitable for sealing to glass the steel shouldhave a coefiicient of expansion over the temperature range of 530 to 30C. of less than 12.5)(10' in./in./ 0., preferably being within the rangeof about 11.5 to 12.5 10' in./in./ C.

I have discovered that chromium steels within the range of 9 to 11%chromium are completely ferritic after heating to 1200" C. if the carbonis maintained below .03% along with titanium in the amount of at least10 times the carbon content and preferably at least .35 aluminum withinthe range of .02 to 30%, silicon .10 to 1.00% and manganese .10 to1.00%. Titanium should be maintained below 1% because of its unfavorableeffect on cleanliness or homogeneity when present in excess amounts.Phosphorus and sulphur should be maintained as low as possible.Molybdenum may be added if desired. Small quantities of nickel, boron,vanadium and tungsten are not desirable,

I United States Patent 2,736,649 Patented Feb. 28, 1956 ICC but may betolerated. The balance of the alloy is substantially iron. Moreover,such steels have a coefiicient of expansion within the temperature rangeof 530 to 30 C. of 11.5 to 12.5)(10' in./in./ C.

Specific examples of steels typical of this invention are set forth inthe following table:

Table I Mn Si Ti C Cr P S Ni Al Table II Ti Al Si Ni However, when thesesteels were decarburized to a .03 maximum carbon content, they wereobserved by microscopic examination to be fully ferritic.

This application is a continuation-in-part of my copending applicationSerial No. 316,327, filed October 22, 1952, now abandoned.

While I have shown and described several specific embodiments of myinvention, it will be understood that these embodiments are merely forthe purpose of illustration and description and that various other formsmay be devised within the scope of my invention, as defined in theappended claims.

I claim:

1. A ferritic stainless steel containing 9 to 11% chromium, .03% maximumcarbon, titanium at least 10 times carbon but not over 1%, .02 to 30%aluminum and .10 to 1.00% manganese, balance iron except for residualirnpurities and elements in amounts that do not adversely affect theproperties.

2. A ferritic stainless steel containing 9 to 11% ohmmium, .03% maximumcarbon, at least .35 but not over 1% titanium, .02 to 30% aluminum and.10 to 1.00% manganese, balance iron except for residual impurities andelements in amounts that do not adversely affect the properties.

3. A ferritic stainless steel consisting essentially of 9 to 11%chromium, .03% maximum carbon, .35 minimum but not over 1% titanium, .02to 30% aluminum, .10 to 1.00% manganese, balance iron except forimpurities and minor amounts of nickel, boron, vanadium, tungsten ormolybdenum.

4. A ferritic stainless steel consisting of about 9 to 11% chromium, 03%maximum carbon, titanium at least 10 times carbon but not over 1%,, .02to 30% aluminum, .10 to 1.00% manganese, balance iron except forimpurities and minor amounts of nickel, boron, vanadium, tungsten ormolybdenum.

No references cited.

1. A FERRITIC STAINLESS STEEL CONTAINING 9 TO 11% CHROMIUM, .03% MAXIMUMCARBON TITANIUM AT LEAST 10 TIMES CARBON BUT NOT OVER 1%, .02 TO .30%ALUMINUM AND .10 TO 1.00% MANGANESE, BALANCE IRON EXCEPT FOR RESIDUALIMPURITIES AND ELEMENTS IN AMOUNTS THAT DO NOT ADVERSELY AFFECT THEPROPERTIES.